function animate(obj,target,callback){
    clearInterval(obj.timer);
    obj.timer=setInterval(function(){
        let step=(target-obj.offsetLeft)/10;
        step=step>0?Math.ceil(step):Math.floor(step);
        if(obj.offsetLeft==target){
            clearInterval(obj.timer);
            if(callback){
                callback();
            }
        }
        obj.style.left=obj.offsetLeft+step+'px'
    },30);
}